Rick's Free Auto Repair Advice

Can you use universal antifreeze?

Using universal antifreeze is a really bad idea

Most auto parts stores sell “all makes, all models” universal antifreeze. But car makers say there’s there’s really no such thing as a universal. How could there be such a thing when every year, make, model and engine uses a different combination of metal, plastic and rubber components? The unique combination of materials in each engine/cooling system design is whey every car maker recommends their own specific antifreeze’ and the specifications are unique to the types of metals, plastics, and rubber used throughout the car’s cooling system.

To qualify for the “all makes, all models” universal coolant moniker, manufacturers must include a dash of every type of corrosion inhibitor available, and many of those inhibitors are incompatible with the materials used in your particular engine.

What’s in antifreeze coolant?

Most manufacturer-specific antifreeze coolant formulas use an 85-95% concentration of Ethylene Glycol as the base chemical . Ethylene Glycol prevents freezing and overheating, but doesn’t provide any corrosion protection. Corrosion protection inhibitor additives are what makes up the other 5 to 15% of the mix.

Corrosion inhibitors protect against metal corrosion, galvanic action and cavitation erosion and the inhibitors used must also be compatible with rubber and plastic seals, gaskets and fittings.

There are two types of antifreeze corrosion inhibitors — Inorganic and organic

Inorganic Additive Technology (IAT) green coolant

The old green IAT coolant is based on ethylene glycol or propylene glycol with corrosion inhibitors like sodium or potassium salts of inorganic anions like: Phosphate, borate, silicate, nitrite, and nitrate. A given coolant formula contains varying
amounts of two or more of these chemicals. The formula usually contains an azole compound like tolyltriazole, benzotriazole, or mercaptobenzothiazole as a copper corrosion inhibitor.

Silicate and phosphate corrosion inhibitors are fast acting so they get to work quickly to protect bare iron and aluminum surfaces. These corrosion inhibitors are proven effective and are generally trouble free. However, because they preciptate out of solution to passivate cooling system components, they have a short life of just two year and less than 30,000 miles.

Phosphate is an anodic inorganic corrosion inhibitor that works well to protect aluminum and cast iron components from corrosion. Phosphate acts as a pH buffer and is often used by Japanese car makers. However, phosphates react poorly with hard water and can form scale in the cooling system which can plug up the radiator and heater core.

image of antifreeze adding to radiator

Typical green silicate antifreeze

Silicate works well to protect aluminum and cast iron engine and cooling system parts from corrosion. It reacts with cooling system metals to form a protective anode film that is literally adsorbed into the metal to “passivate” it. It works because it is an ANODIC inhibitor. As soon as the anodic film layer becomes higher than the cathode current density, the metal components are “passivated.” The silicate film is insoluble and impermeable.

The downside of silicate is that it has a short life so you have to flush it and refill about every two years. Silicate antifreeze is also prone to gelling. The worst part is that silicate is abrasive and damages water pump seals. Silicate formulas are often used in European cars

Nitrates components to form a Nitrosamine passivation film. But nitrates have a short life and don’t work well on aluminum or aluminum alloys.

Borate is also an anodic corrosion inhibitors that works best with cast iron engine parts, but is corrosive to aluminum and aluminum alloys

However, it’s important to understand that anodic corrosion inhibitor concentration must be high enough to reach the passivation threshold to protect engine and cooling system metals. Many all makes, all models universal antifreeze formulas don’t contain high enough silicate levels to reach that point. An antifreeze with too low a concentration of anodic corrosion inhibitor is worse than having no anodic inhibitor at all. That results in an anode film that’s too thin to provide passivity, resulting in pitting and accelerated corrosion.

Organic Acid Cathodic corrosion inhibitors

Cathodic corrosion inhibitors prevent the cathodic reaction with the metal components. To achieve this, the antifreeze contains metal ions that precipitate on cathodic metal within the engine and cooling system, forming an adherent film. Some examples of inorganic cathodic inhibitors are the ions of magnesium, zinc, and nickel.

Common organic corrosion inhibitors

Organic acid corrosion (OAC) inhibitors or organic acid technology (OAT) coolant can act as cathodic or anodic inhibitors, or a combination of the two. Common organic acid compounds are: 2-ethylhexanoic acid, sebacic acid, azelaic amines, urea, Mercaptobenzothiazole (MBT), benzotriazole e toliotriazol, aldehydes, heterocyclic nitrogen compounds, sulfur-containing compounds and acetylenic compounds and also ascorbic acid, succinic acid, tryptamine, caffeine and extracts of natural substances. OAT coolants also contain an azole additive as a copper corrosion inhibitor.

Organic acid compounds are film-forming with a strong

organic acid antifreeze versus universal antifreeze

Organic acid antifreeze comes in different colors

affinity for metal surfaces. Organic acid formulas develop a protective hydrophobic film on the metals to form a barrier. They offer much longer life than inorganic inhibitors, but take much longer to form a protective film than inorganic inhibitors.

Organic acid inhibitors protect aluminum and cast iron components. They are non-abrasive, so they don’t damage water pump seals. However, the exact formulation MUST be compatible with the plastic and rubber components used in a particular engine/cooling system combination.

Since car makers vary the types of rubber and plastics by year, make, model and engine, there are simply too many variations for any antifreeze manufacturer to claim their product works in all makes, all models and is universal.

Some car makers recommend Hybrid Organic Acid (HOAT) antifreeze formulas that use an organic anion as the primary corrosion inhibitor, along with an inorganic corrosion inhibitor. HOAT, for example, may use organic acid with a low silicate inorganic corrosion inhibitors. The inorganic corrosion inhibitor provides rapid passivation until the organic acid portion can take full effect. Yet the low silicate concentration doesn’t damage water pump seals. HOAT coolants also contain an azole additive as a copper corrosion inhibitor.

How can antifreeze manufacturers claim their product is all makes, all models or universal?

They really can’t. Generally, all makes all models universal antifreeze is 96% ethylene glycol and just 2 to 5% inhibitors. Since the product is billed as all makes, all models, it’s can’t possibly be vehicle specific, so it really provides LESS corrosion protection than the factory formula. To cover their bases, these all makes, all models universal antifreeze formulas use a small amount of every inorganic inhibitor, which causes corrosion by itself because the inhibitors interact poorly with each other.

use the correct coolant, never a universal antifreeze

In fact, many car makers have issued service bulletins warning not to use the wrong antifreeze just for this reason. In addition to interactions between inorganic inhibitors, there’s also the issue of incompatibility between the all makes, all models universal antifreeze and the rubber and plastics used in the engine and cooling system components.

So mixing different types of antifreeze coolants or add the wrong antifreeze coolant can actually CAUSE corrosion, pitting of water pump, rust formation in radiator and total cooling system degradation.

Using the wrong antifreeze coolant can cause extensive cooling system damage

Shops like to use all makes, all models antifreeze coolant because they don’t have to stock vehicle specific antifreeze or tie up their repair bay waiting for an antifreeze delivery from the local dealer. However, if a shop uses all makes, all models universal antifreeze coolant in your vehicle and it’s not fully compatible the damage won’t show up for at least a year. By then you won’t connect the dots to realize that the coolant flush with the wrong coolant is what damaged your radiator, heater core or water pump. Good luck pointing the finger at the shop at that point!

Why do shops and parts stores sell and use a universal or multi-vehicle coolant?

Simple, shops and auto parts retailers don’t have the shelf space to stock every car maker’s specific type of coolant. Many universal or multi-vehicle coolants have a neutral color, neither bright green nor orange. If the vehicle is just low on coolant and you’re using a universal coolant to top off the level, you probably won’t compromise the anti corrosive capabilities since the system is already passivated. However, there’s no way of knowing if the new universal coolant is compatible with the corrosion additive package which could result in corrosion inhibitor drop out.

warning about using a universal antifreeze in your car

Which water to use when mixing antifreeze concentrate or topping off the system?

Ask any car buff which water to use when mixing antifreeze concentrate or topping off  a cooling system, and they’ll tell you to use distilled water. Well, that’s certainly better than hard tap water. But distilled water can still contain minerals that can react with metal and your antifreeze to form corrosion and deposits. You want de-ionized/de-mineralize water.

Other antifreeze additives

In addition to corrosion inhibitors, all antifreeze formulas contain an anti-oxidant, anti-cavitation and anti-foaming additive, along with a identifying dye.

What determines antifreeze life?

Ethylene Glycol never wears out, but the corrosion inhibitor,anti-oxidant, anti-cavitation and anti-foaming additives do wear out. How long the antifreeze lasts is directly related to type and amount of the corrosion inhibitor in the formula. If you don’t change your antifreeze coolant at the recommended intervals, you risk causing extensive and expensive damage to your radiator, heater core, heater tubing and water pump.

©, 2017 Rick Muscoplat



Posted on by Rick Muscoplat

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